Soybeans and soybean processed food products are important protein sources in the diet, and various components thereof are known to have biological regulatory functions. 7S Globulin is an important constituent component of soybean protein, but has been found that its content in soybean protein is low. According to general knowledge, soybeans contain 7S and 11S globulins in the ratio of 1:2. In addition to these globulins, it has been reported that oil-body-associated protein is also present in soybeans and its content amounts to about 35% by weight of industrially produced soybean protein isolate (SAMOTO, Biosci. Biotechnol. Bioche, Vol. 62, No. 5, 935-940, 1988). This indicates that 7S globulin does not exceed one-third of soybean protein.
It has also been reported that soybean 7S globulin has a reducing function of serum triglycerides (OKITA, J. Nutr, Sci. Vitaminol., 27, 379-388, 1981; and AOYAMA, Biosci. Biotechnol. Bioche, Vol. 65, No. 5, 1071-1075, 2001). High levels of serum triglycerides cause hyperlipemia and even arteriosclerosis, which results in cerebral and cardiovascular diseases. Therefore, the reduction of serum triglycerides is of great significance.
With the diversification of the diet, consumption of animal food is increasing and the intake balance between animal food and vegetable food is disrupting. It is thus not always easy to take 7S globulin from general foodstuffs at an amount of 5 g or more, which is an effective amount for reducing serum triglycerides (KAMBARA, Therapeutic, Research, vol. 23, no. 1, 85-89, 2002).
It is very useful if soybean 7S globulin can be readily taken in the form of a powder beverage prepared by mixing the globulin with water or the like.
However, since a protein isolate which is rich in soybean 7S globulin (hereinafter referred to as soybean 7S protein isolate) has remarkably high viscosity and high hydration properties, its powder forms undissolved lumps when mixed with a liquid such as water. In addition, undissolved lumps once formed are very difficult to disperse and require strong stirring to break them, which preclude the convenient and simple intake of soybean 7S protein. These physical properties of a soybean 7S protein isolate also result in poor workability when used in water-containing dough, and less easiness to eat when used in chewable tablets or the like.